The present invention relates to a measuring frame for contactless optical determination of a gunshot position of a bullet through a target surface. Furthermore, the present invention also relates to a pertaining measurement and evaluation process. In addition, the present invention relates to a display system that uses at least one such measuring frame.
Measuring frames that determine a gunshot position by means of contactless light barrier technology have been used among sports shooters and for the training of shooters for quite some time. In such optical measurement processes, a bullet that flies through the measuring frame is measured in a contactless way by means of infrared barriers. An individual infrared barrier is thereby composed of an infrared sender that sends infrared light in a focused light beam, and an infrared receiver that is situated opposite to the infrared sender and that measures the brightness of the incoming infrared light beam. Depending on the size of the measuring frames, up to 500 independent light barriers are installed and arranged in a solid grid screen on the internal sides of the frame.
The infrared senders of the individual light barriers create a continuous light curtain within the frame. If a bullet flies through this light curtain, several light barriers are interrupted partially or completely both on the horizontal X-axis as well as on the vertical Y-axis of the measuring frame.
The advantage of the solution consists on one hand of the absence of wear as no consumables such as paper or rubber bands are involved. On the other hand, the use of optical measuring frames has the advantage of high measurement accuracy and a low susceptibility with regard to contamination and temperature variations.
Such linear measuring frames are known for example from the DE 4115995 A1 or the EP 034284 A1. From the U.S. 2012 0194802 A1, also a combined measurement device is known that uses two crossing optical light barriers to cover the innermost target area, and an acoustic process to determine a gunshot position in an outside area. Thereby, a series of light receivers that are arranged on a circular arc segment are used to determine the intensity of the radiation, which is emitted from a light sender that is located opposite to them, on the diverse points of the circular arc. The gunshot position is determined based on the different brightness values.
However, there is still the need to indicate measurement frames with increased levels of accuracy and robustness that can be produced in a cost-efficient way and that are not made of any wear materials such as acoustic membranes while being still compliant with the maximum permitted dimensions for measuring frames of this type.